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Scanned continuous wave CO2 laser resurfacing: a closer look at the different scanning modes
S C Huilgol1, E Poon, E Calonje
1Dermatological Surgery and Laser Unit and Dermatopathology Unit, St. John's Institute of Dermatology, St. Thomas' Hospital, London, England.
Background:
The immediate effects of CO2 laser resurfacing include tissue ablation and residual thermal damage. These laser-tissue interactions are shaped by parameters including fluence, dwell time, and number of passes.
Objective:
To assess the vaporization depth and residual thermal damage following use of the "superficial" or "deep" scanning modes of a 40 W continuous wave CO2 laser using both frozen and paraffin sections.
Methods:
Fourteen subjects were divided into two groups for test treatments in the right preauricular area with two passes of the laser. The "superficial" mode parameters were 10 mm2 scan, 200 mm lens, power 36 W, scan time 0.24 seconds, dwell time 0.22 msec, and fluence 5.5 J/cm2. The "deep" mode settings were 9 mm2 scan, 200 mm lens, power 18 W, scan time 0.64 seconds, dwell time 0.28 msec, and fluence 7.0 J/cm2. The deep mode has a greater pattern density than the superficial mode and also has a double pattern of exposure. Biopsies encompassing equal areas of treated and untreated skin were taken immediately postoperatively and processed with both frozen and paraffin-embedded techniques.
Results:
Vaporization depth was similar in both scanning modes and by both tissue-processing techniques. On frozen sections, residual thermal damage was 20% greater in the deep mode than the superficial mode, but this was not a statistically significant difference. There was no significant difference between the two modes in the depth of thermal injury on paraffin sections.
Conclusion:
In keeping with theoretical expectations, vaporization depth was similar in both treatment groups. No significant difference in residual thermal damage could be demonstrated between the two modes. However, the results on frozen sections suggest that residual thermal damage may be greater in the deep mode than in the superficial mode. In addition, frozen sections may be more sensitive than paraffin sections in the detection of residual thermal damage following laser resurfacing.
